They’ll always be someone quicker than you, and someone will always be “last” in a group ride. Such is life.
Speed and distance goals don’t really work off road as the terrain is so hard to compare, however.
To ride faster, simply ride faster. Maybe try a shorter route than normal at a quicker pace. Maybe do two short loops at different speeds to evaluate what you feel comfortable at.
Unless the planned ride is a few months off nothing in the short term will make you quicker, just enjoy it.